A conventional wheel nut, stud or bolt comprises a head portion designed to receive a wheel spanner, a threaded portion to screw onto the wheel axle flange and a tapered cone portion shaped to engage in a matching shaped recess provided in the wheel. Sometimes the cone portion is provided separate from the head portion and sometimes the fastener is further provided with a conventional loose washer behind the cone.
In whatever form the wheel fastener is conventionally made, when tightened a high degree of friction is involved, namely, friction on the threaded portion, friction on the wheel recess and friction on the cone portion contacting the wheel recess. This latter friction is particularly high, and tends to be greater during loosening than during tightening, ie., it requires more torque to loosen the fastener than to tighten the same fastener. This is the primary reason why conventional wheel nuts are often so hard to remove. It is also necessary to apply a large torque to a conventional wheel nut during fastening in order to overcome the friction and still obtain the necessary hold-down pressure. Conventionally, friction is assumed and even taught to be necessary and is relied upon to hold the fastener securely, however a recent discovery suggests that this need not be the case.
These problems with conventional wheel fasteners become critical in relation to racing cars where rapid and effective wheel changes must be performed in race time. A stubborn wheel fastener will cause loss of valuable time that could be the difference between winning and losing. Furthermore, it is essential that the correct torque be applied to the wheel fasteners when tightened, and this can be difficult to achieve in the very short time available, with conventional fasteners.
The present invention was developed with a view to providing a fastener bearing assembly that can be used with wheel fasteners to virtually eliminate a high proportion of the friction between a conventional wheel fastener cone, and the wheel fastener recess. In one embodiment, the invention also provides a wheel fastener which incorporates the bearing assembly therein. Although the invention will be described with particular reference to automotive wheel and engine head fasteners, it is to be understood that the fastener bearing assembly is not limited to automotive fasteners and can be used in any application to minimise friction between a fastener and the object to be fastened.
A further problem with conventional wheel fasteners is the problem of theft of vehicle wheels or inadvertent loosening of the wheels while driving. Conventional wheel nuts/studs can be relatively easily removed with an appropriate wheel brace once the hub cap is removed. Various means have been proposed to improve security and inhibit thieves, including the provision of a key operated lock in a wheel stud and/or the hub cap. This type of lock is not entirely satisfactory as it requires the vehicle operator to carry an additional key as well as a conventional wheel brace.
The problem of on-road loosening of wheel fasteners is particularly acute with long-haul trucks and other transport vehicles which have a large number of wheels that not infrequently require replacement. If the wheel fasteners have not been properly fastened during replacement of a wheel they can work loose and instances of a truck wheel actually falling off in transit are not uncommon.
The present invention was also developed with a view to providing a novel fastener that can be secured more effectively against unauthorised or inadvertent loosening.